Image reproduction with mercurous halide

ABSTRACT

A PROCESS FOR PREPARING A LIGHT-SENSITIVE ELEMENT BY PRECIPITATING MERCUROUS IODIDE SUBSTANTIALLY FREE OF MERCURIC IONS FROM STOICHIOMETRIC AMOUNTS OF MERCUROUS NITRATE IN A NITRIC ACID SOLUTION AND POTASSIUM IODIDE, CONDITIONING THE RESULTING MERCUROUS IODIDE AND COATING IT ON A SUPPORT. THE PRECIPITATION OCCURS IN THE PRESENCE OF AQUEOUS POLYVINYL ALCOHOL OR INERT GELATIN.

United States Patent 01 fice 3,597,205 Patented Aug. 3, 1971 3,597,205 IMAGE REPRODUCTION WITH MERCUROUS HALIDE Gordon N. Flannagan, Fair Haven, N.J., assignor to E. I. du Pont de Nemours and Company, Wiimington, Del. No Drawing. Filed Nov. 2, 1967, Ser. No. 679,983

Int. Cl. G03c 5/38 US. CI. 96-48 2 Claims ABSTRACT OF THE DISCLOSURE A process for preparing a light-sensitive element by precipitating mercurous iodide substantially free of mercuric ions from stoichiometric amounts of mercurous nitrate in a nitric acid solution and potassium iodide, conditioning the resulting mercurous iodide and coating it on a support. The precipitation occurs in the presence of aqueous polyvinyl alcohol or inert gelatin.

BACKGROUND OF THE INVENTION The use of mercury compounds in photographic emulsions is old in the art. These compounds have been used as photographic sensitizers. Photographic emulsions have also been examined using light-sensitive mercurous iodide but these were found to be impossible to develop and fix. Suzuki and Nogue, Kogyo Kuzaku Zusshi (Journal of the Chemical Society of Japan, Industrial Chemical Section), 66 (10): 1419-1423 (1963). It has now been found that a photosensitive mercurous halide emulsion free of silver and substantially free of mercuric ion can be used to produce developable latent and print out images which are stable.

SUMMARY OF THE INVENTION When practicing this invention, procedures for preparing mercurous halide emulsions follow the silver halide technology, namely, precipitation, ripening, coagulation, washing, separation, dispersion, digestion and coating.

The precipitation of the mercurous halide is performed by adding mercurous nitrate dissolved in HNO (generally about 1 N) to a dilute alkali metal halide gelatin solution usually 0.6 to 0.8 part by weight of alkali metal halide per part of hydrated mercurous nitrate. Stoichiometric amounts of mercurous salt to potassium halide should be used. Preferably potassium halide is used to prepare the mercurous halide.

The mercurous halide may be further conditioned by ripening, washing and digesting to improve its light sensitivity. Ripening is generally at a temperature of 120 F. for one hour. To form curds, an organic polymer, generally the acetal of polyvinyl alcohol and sulfonated benzaldehyde as indicated in US. Pat. 2,772,165, is present in an amount of from 3% to 20% by weight of the protein present. After coagulation and settling, the curds are separated by decanting followed by redispersion f the curds by adding a mixture of 10% gelatin in Water. The emulsion is then digested for one hour at 120 F., cooled to 90 F, coated on a suitable support, and allowed to dry. The coated element has a weight ratio of mercurous halide to binder of about 5:1 to 0.1:1 and preferably about 1:1.

The emulsion may be mercurous iodide, mercurous bromide, mercurous chloride, or mixtures thereof. The mercurous iodide emulsions are preferred because they have the best speed characteristics and exhibit the least fog. To produce the desired effects of this invention, high purity chemicals should be used. The mercurous salt used must be essentially free of mercuric ion to avoid severe or fatal loss in speed. It is also essential to keep out impurities which will complex with mercuric ion to react and form dark compounds such as mercuric sulfide. If a gelatin binder is used, it should be an inert gelatin which is free of impurities that will reduce the mercurous halide, for example, pig-skin gelatin contains impurities which result in a loss of speed and high fogging.

Other standard emulsion additives can be added to the mercurous halide mixtures. Chemical sensitization with chemical sensitizers used for silver halides produced improvement in the speed. Satisfactory results were obtained using gold sensitization, stannous chloride sensitization, sulfur sensitization with conventional organo-sulfur sensitizers, sodium thiosulfate, etc., and others such as those disclosed in US. Pats. 2,423,549; 2,540,086; and 3,026,203.

Optical sensitization of mercurous halides can be achieved by sensitizing the emulsion with conventional optical sensitizers such as merocyanine dyes and other dyes such as those disclosed in US. Pats. 2,342,546 and 2,704,717.

The emulsion can contain known antifoggants, e.g., benzotriazole, 2-mercaptothiazoline, triazaindenes, etc., as Well as the usual hardeners, e.g., chrome alum, formaldehyde, dimethylol urea, etc., and other emulsion additives such as surfactants, toners etc.

A binder is preferably present to aid in holding the mercurous halide on the support. The preferred binders are inert gelatin and water-soluble polyvinyl alcohol but other natural or synthetic water-permeable organic colloid binding agents can be used. Inert gelatin is lime process bone gelatin devoid of added sulfur sensitizers, restrainers, etc. Other binders include the derivatives of water-soluble polyvinyl alcohol, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers, etc.

The preferred support is polyester terephthalate such as those disclosed in US. Pat. 2,779,684, British Pat. 766,290 and Canadian Pat. 562,672. Suitable supports may be any transparent plastic such as cellulose acetate, cellulose triacetate, and other cellulose mixed esters; polymerized vinyl compounds, other films as disclosed in US. Pats. 3,052,543; 3,072,496; paper and glass.

Any source of actinic radiation is suitable as the exposure source for this invention. Suitable sources include photographic flood lamps, mercury-vapor lamps, carbon arcs, X-rays, etc.

Development of a latent image in the mercurous halide emulsion appears to follow the mechanisms of silver halide development. The active ingredients in developers tested appeared to be Metol andhydroquinone. Conventional silver halide developers containing these constituents produced images at development rates which paralleled silver halide development. Conventional developers containing ascorbic acid and 1-phenyl-4-methyl-3-pyrazolidone at a pH of 10.5 produced good images. Conventional X-ray film developers also worked satisfactorily. Generally, emulsions of mercurous halide tend to fog rapidly on development. To reduce fogging characteristics, various antifoggants can be added to the developers, Suitable antifoggants include 5-nitrobenzimidazole nitrate, 2-mercaptothiazoline, etc.

Other developers such as those disclosed in Wall and Johnson, Photographic Facts and Formulas, American Photographic Publishing Co., Boston (1947) especially those on pages 55, 56, 63, 65 and 66 produced satisfactory images although development in some of the tested developers was slower than in others.

Permanent developed images are prepared by reversal processing which is accomplished by fixing or bleaching with a selective oxidation agent for the developed image (e.g. an ammonium persulfate solution) and subsequent transformation of the remaining mercurous salt to a dark image. Satisfactory fixing is accomplished by immersing developed images (eg. generally about one minute) in an aqueous solution containing ammonium persulfate and optionally containing 10% sodium nitrate. Darkening of the unexposed areas can be achieved by immersing the film in a dilute, approximately 2% ammo nium polysulfide solution or in a silver halide developer which will turn the non-exposed areas black. When using the selective oxidation procedure as outlined above, the film after oxidation may be treated with a dilute potassium iodide solution, generally 5%, to enhance the direct positive. Therefore, after fixing by selective oxidation, darkening of the image (increase contrast) can be achieved by either (1) developing in the presence of a strong reducing agent, i.e., silver halide developers, (2) metathetical substitution, i.e., further treatment in ammonium polysulfide to form mercurous sulfide or (3) complexing, i.e., treatment in dilute potassium iodide. The process of selective oxidation will be further illustrated by reference to the examples,

This invention will be further illustrated but is not intended to be limited by the following examples.

Example 1 A mercurous halide emulsion was prepared under red safelights and contained the following:

G. Mercurous nitrate [Hg (NO 2H O] 5 Potassium iodide 3 12% polyvinyl alcohol aqueous solution 40 The mercurous nitrate was added to the polyvinyl alcohol under vigorous stirring followed by a slow addition, while stirring, of the potassium iodide. The resulting mercurous iodide emulsion was coated on a resin subbed polyethylene terephthalate support such as that described in Example IV, U.S. Pat. 2,779,684. The coated support was allowed to dry resulting in a photosensitive mercurous halide emulsion approximately 0.0005 inch thick. The photosensitive element was exposed to a National Bureau of Standards Test Chart with a mercury vapor lamp operating at 35004200 A., at a one inch distance for one second. The results of the exposure was a latent image which was developable in a commercially available Metol-hydroquinone X-ray developer.

The exposed element was immersed in the developer for 3 minutes resulting in images which were dark in color against a yellow background. The developed images would fog after long exposures to room light, unless the images were fixed as in Example 3.

By increasing the length of exposure, print-out images could be obtained by exposures to the mercury vapor lamp. However, the image would fade in several days unless developed as above.

Example 2 A photosensitive mercurous halide emulsion was prepared as described above and contained the following:

Part A:

Potassium iodide3.5 g.

Gelatin (inert)--1.0 g.

Distilled water-25.0 cc. Part B:

1 N nitric acid .0 cc.

Mercurous nitrate [Hg (NO -2H O]5.0 g. Part C:

10% polyvinyl acetal polymer1.0 cc. Part D:

10% gelatin-water mixture60.0 g.

The polyvinyl acetal polymer used in Part C is a polyvinyl acetal organic polymer as is disclosed in U.S. Pat. 2,772,165.

The components of Part A were mixed and heated to 120 F. Part C was added while stirring and the pH ading until precipitation was complete. The mixture of Parts A and B was then ripened by stirring for one hour at 120 F. Prat C was added while stirring and the pH adjusted at F. to 3.0 with l N sodium hydroxide. The gelatino-mercurous halide mixture was allowed to settle and the supernatant liquid decanted to remove dissolved salts. Part D was added to the residue and the mixture was digested for 1% hours at 20 F. The emulsion was coated on a polyethylene terephthalate support as in Example 1.

After drying the photosensitive element was exposed as in Example 1 and developed for 1 minute in a commercially available hydroquinone, 1-phenyl-4-methyl-3-pyrazolidone, X-ray developer. Results were the same as in Example 1.

Example 3 Developed images may be fixed into a direct positive by selective oxidation of the mercury image leaving the mercurous iodide in the film in inverse ratio to the exposure.

A fixing solution was prepared as follows:

SOLUTION A Ammonium persulfate50 g. Soduim nitrate50 g. Water-500 ml.

Developed images were prepared as in Example 1 and were then immersed in Solution A at room temperature for one minute. The image area became bleached. The film was washed in running water and then dipped into a 2% acqueous ammonium polysulfide solution. This produced a stable positive black image.

Example 4 A 60-gram sample of the mercurous halide emulsion, as prepared in Example 2, was used to test the effect of chemical sensitization. A solution containing sodium thiosulfate (70 g./l.) was prepared. Two milliliters of this solution were then added to the 60-gram emulsion sample. The mixture was stirred for two hours at 120 F. The emulsion was then coated on a resin subbed polyethylene terephthalate support as in Example 1. A sample of the unsensitized emulsion from Example 2, and the sensitized emulsion of this example were then exposed as in Exam pie 1 for & of a second. The exposed elements were then developed as in Example 1. A visible image occurred in the sensitized emulsion while no image was obtained for the unsensitized emulsion.

Example 5 An emulsion was prepared as in Example 1 and was divided into two equal parts. One part was optically sensitized by adding 6 ml. of a solution containing 0.5 mg./ml. of 3,3-diethyll0 methyl-[2,3-napthio]-carbocyanine toluenesulfonate dye, prepared as disclosed in U.S. Pat. 2,704,717. This portion was then stirred for 10 minutes at 120 F. before being coated on the base as described in Example 1. The unsensitized and sensitized samples were then exposed through a step with a Wratten No. 29 filter at a distance of 21 inches from a photofiood bulb operating at volts for 10 seconds. The exposed samples were developed as in Example 1. Two more steps were visible with the sensitized emulsion than could be seen in the unsensitized product.

Example 6 Example 5 was repeated except that 3 ml. of a merocyanine dye (0.5 mg./ml. of acetone) as prepared according to Example 1, U.S. Pat. 2,342,546 was added to the emulsion sample. The sensitized and unsensitized samples were then coated as in Example 5. The samples were then exposed with 550 m light for various periods of time with a Bausch and Lomb high intensity monochromater. After the samples were developed as in Example 1, it became apparent that the sensitized sample showed much stronger sensitivity for the 550 m monochromatic light. The unsensitized control sample produced developable latent images only at exposures of ten seconds whereas the sensitized sample produced developable latent images at exposures of one second.

Example 7 An emulsion coating was prepared as in Example 1 and was divided into two parts, one to serve as a control. Two samples of the developer used in Example 1 were prepared. An antifoggant, S-nitrobenzimidazole nitrate (1 g./liter) was added to one of the developer samples, the other serving as a control. The coated samples were exposed as in Example 1. Appreciable background fog was present in the control sample which was developed in the control developer for one minute. The other sample when developed in the developer containing the antifoggant for periods up to three minutes developed without any appreciable fog. The developed image was improved accordingly,

1. In a process for image reproduction from a lightsensitive element which comprises a support and a layer containing mercurous halide in an inert gelatin, a watersoiuble polyvinyl alcohol or a partially hydrolyzed polyvinyl acetate binder composition as the sole image producing component, said mercurous halide composition being essentially free of silver and mercuric ions to give a latent, developable image upon exposure, which comprises imagewise exposing said element and developing said element in a silver halide developer solution, the improvement of fixing said developed element in an aqueous solution of ammonium persulfate to remove the exposed image area and give a direct-positive image from Examples 15 the unexposed mercurous halide.

2. The rocess defined in claim 1 includin the st Example 2 was repeated except that the halide in of treatinopsaid ositive fixed ima i ep Part A of Example 2 was changed in accordance with P g6 a 1 u 6 aqueous the table below Coating was the Same as in Example solution of ammonium polysulfide, a d1lute acquous solu- 2 The developers and developer times are indicated 20 tron of potassium iodide or with a silver halide developer low. The results of the developed images were similar to give better contrast to said direct-positive image. to those obtained in Examples 1 and 2.

TABLE 1 Part A Emulsion Exposure Developer Example N0. Additive Amount, g. color time Developer time 8 KBr llll 2.6 White 1 see Same as Ex. 1 1min.

9 {KBr 2.6 Slight 1 see Same as Ex. 2 1 min. KI 0.2 Yellow lsec J10 1 min. 10 KCl 1.5 White 1 min Same as Ex. 1 15 sec. 11 .{KCl 1. 4 Slight 1 sec Same as Ex. 2 10 see KI 0.4 Yellow 1 sec do 10sec 1 Except antifoggant, 70.05 g. l/l. of 2mercaptothiazoline, added.

As can be seen above, the chloride emulsion was generally much slower than the other emulsions. Likewise, the chloride emulsions had a greater tendency to fog thereby necessitating the presence of an antifoggant in the developer or in the emulsion.

This invention provides a new system of photography that could replace certain silver halide products. Thus, the demand for silver for certain products could be eased.

This invention also provides the advantage of producing good developable images in a nonsilver halide system using essentially the same technology as is used in silver halide systems. Furthermore, this invention provides the advantage of being able to develop and fix images in mercurous halide emulsions which are convenient and economical to use.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

References Cited UNITED STATES PATENTS 2,095,839 10/1937 Sheppard et al. 96-88 2,732,304 1/1956 Vanselow 9688 2,874,047 2/1959 Meulen et al. 9688 2,933,389 4/1960 Meulen et al. 96-88 3,236,651 2/1966 Marks et al. 9688 U.S. Cl. X.R. 9688, 64 

